Anode and supporting structure therefor



Jan. 10, 1967 scN ET AL 3,297,561

ANODE AND SUPPORTING STRUCTURE THEREFOR Filed May 8, 1962 4 Sheets-$heet 1 1 1b 1 17 1 L A 12 FIG! 1 1o 1 3y W W,Mw/

Jan. 10, 1967 HARRISON ETAL 3,297,561

ANODE AND SUPPORTING STRUCTURE THEREFOR Filed May a, 1962 4 Sheets-Shed 5 FIG. 6

Jan. 10, 1967 G. G. HARRl SON ET AL 3,297,561

ANODE AND SUPPORTING STRUCTURE THEREFOR Filed May 8, 1962 v 4 Sheets-Sheet 4 FIG) Z2 Z7 Z4 22 T w H06 //VV/1/70/?5 United States Patent 3,297,561 ANODE AND SUPPORTING STRUCTURE THEREFOR Geoffrey Granville Harrison and Donald Henry Prince,

Runcorn, England, assignors to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain Filed May 8, 1962, Ser. No. 193,668 Claims priority, application Great Britain, May 8, 1961, 16,592/ 61 11 Claims. (Cl. 204-286) This invention relates to anodes for the production of chlorine by electrolysis of brine, particularly in cells having a substantially horizontal moving mercury cathode.

For many years the Castner-Kellner cell has been widely used for brine electrolysis, and this is largely due to the fact that such cells are comparatively simple and reliable, although one cause of difficulty in these cells has been the anodes which are customarily made of carbon. For various reasons the carbon erodes away in use and the efficiency of the cell deteriorates, particularly because the prime operating cost, electricity, is calculated in Board of Trade units which are based on both current and voltage: the current needed for electrolysis of a given solution is substantially invariable, but the voltage depends upon the distance between the carbon anode and the mercury in the cell, and hence increases with anode erosion. Attempts have been made to avoid the disadvantage of cost increasing with anode wear, for example by minimising anode wear by the use of other materials, but because of the contents of the cell in use, including nascent wet chlorine, mercury, and caustic soda, the choice of suitable materials is restricted.

Recent research in electro-chemistry and metallurgy has established that titanium metal, coated over part of its surface with platinum which acts as an operative anode surface, makes a highly satisfactory material for anodes for this purpose. The high initial cost of the material is compensated by its extremely long life in use, and an additional advantage is that the down time of cells can be reduced.

However, experience has taught that to obtain maximum efiiciency and reliability together with minimum cost, it is not sufficient merely to replace the carbon with a piece of platinised titanium. Nevertheless, it is desirable to convert existing cells to platinised titanium anodes where possible, and the object of the present invention is to provide an anode designed so that it can be used for this purpose.

In accordance with the present invention a titanium anode structure for use in the production of chlorine by electrolysis of brine comprises an operative anode surface of a platinum metal upon mesh made of titanium or a titanium alloy, and a pillar for suspending said mesh in the cell and conducting electrolysing current to the mesh, the end of the pillar adjacent to the mesh being spaced from the mesh so that chlorine liberated by electrolysis in the vicinity of the pillar end is not trapped but can pass through the mesh and make its way past the pillar to exit from the cell by way of the space between the mesh and the pillar end.

The platinum metal coating making up the operative anode surface may be platinum itself or another noble metal or alloy thereof which functions similarly. It is preferred to use platinum, rhodium, iridium, or alloys of two or more of these metals, particularly those containing platinum itself. The platinum metal may be deposited on one or both faces of the mesh.

For the purpose of the present invention, the term mesh is intended to include any thin sheet form of the metal in which a large number of holes or spaces provide free passage through the thickness of the sheet between its opposing faces. The term thus includes materials of woven form, for example wire mesh and gauze, punched or slotted metal sheet, aand the material known as expanded metal, made by cutting a series of slots in sheet metal and then stretching the sheet so as to increase its overall area and form a multiplicity of spaces therein.

The brines to be electrolysed using the anodes of the present invention are those well known in the art, and are generally aqueous solutions of sodium or potassium chlorides, which may be natural or artificial and may have been treated to any desired extent in order to remove undesirable impurities.

The pillar may be of any convenient form and may be secured in the cell and connected to -a source of electrolysing current in conventional manner. The pillar may, for example, be a solid shaft but is preferably a titanium or titanium alloy tube.

The spacing of the pillar end from the mesh may be achieved especially well by securing the pillar to an end plate or block which is supported in spaced relationship to the mesh and is secured at its edges to stilfeners carried by or upon the mesh.

The stiffeners may themselves be the means for supporting the end plate or block in spaced relationship to the mesh. Especially suitable stiffeners, both for economy and efliciency, are strips secured edge-on to the mesh; such strips may be bent and two or more of them may be joined together in any convenient manner to provide any desired degree of stiffening for the mesh and to provide an adequately strong joint with the end plate or block.

In order to avoid the stiffener strips trapping gas in the space between the pillar end and the mesh, care should be taken to make sure that some gap is left which provides communication between the main body of brine electrolyte and the space separating pillar end and mesh. This may be achieved for example by surrounding the pillar end (or end plate or block) only partially by the supporting members, or by leaving gaps in the supporting members or in the end plate or block.

It is preferred that, apart from the platinum metal surface, all parts of the anode structure in contact with the cell contents are made of titanium or titanium alloy. In this way, corrosion problems are minimised. If it is considered uneconomical to make the more massive parts (particularly the pillar) of solid titanium or titanium alloy, a core of cheaper metal can be used provided that it is not exposed to corrosion by the cell contents.

The anodes of the present invention can be substituted for the conventional graphite anodes very readily, and are simple, robust and satisfactory structures for this purpose. The titanium mesh, on which the operative platinum surface is supported, is immersed in the brine and can readily and accurately be set and maintained in a plane parallel with the mercury cathode surface.

The invention is illustrated but not limited by reference to the accompanying drawings, wherein FIGURE 1 is a sectional elevation and FIGURE 2 is a plan view of one form of anode, FIGURE 3 is a sectional elevation and FIGURE 4 is a plan view of an alternative form of anode based on that of FIGURES l and 2, FIGURES 5 and 6 are views (in plan and part sectional elevation respectively) of an alternative form of construction of an anode in the region of its supporting pillar, FIG- URES 7 and 8 are views (in plan and part sectional 3 elevation repsectively) of a modification of the construction shown in FIGURES 5 and 6 and FIGURE 9 is a plan view of an anode incorporating the constructions shown in FIGURES 5 to 8.

The anode shown in FIGURES 1 and 2 comprises a sheet 10 of titanium mesh having integral side edge portions 11 bent at right-angles to the plane of sheet 10, and corner gussets 12 joining each two side portions 11. This sheet carries on its lower and unobstructed face a layer of a platinum metal (not shown).

Secured to the surface of the sheet 10 and within the area defined by the side portions 11 are four U-shaped stitfeners 13 each made of a length of strip titanium, the stiffener-s being arranged in pairs, base-to-base, and being joined together so that their bases define a pocket or cavity 14. Conveniently, both sheet 10 and cavity 14 can be substantially square or rectangular.

A titanium plate 15 having flanged edges 16 is located in the recess 14, each flanged edge being secured to a different one of the stilfeners 13. The plate is spaced away from the mesh sheet 10, and the corners of the plate are trimmed off so that communication between the spaces below and above the plate is freely possible via openings 17.

A titanium cup 18 is fixed to the plate, the rim 19 of the cup being secured to one end of a cylindrical titanium sleeve 20, for example by a welded joint. If desired, the cup 18 and sleeve 20 can be fabricated to gether as a single unit, so avoiding the need for securing them together.

In FIGURES 3 and 4, the anode represented is essentially a double form of the type of anode represented in FIGURES 1 and 2, and comprises a single sheet provided with two pillar supports. In FIGURES 3 and 4, the reference numbers and parts have the same significance as in the description of FIGURES 1 and 2.

All of the parts so far described are made of titanium or an alloy thereof, and the lower and unobstructed face of the mesh 10 is platinised.

Located within the sleeve and forced into intimate electrically-conducting contact therewith is a copper busbar, not shown.

All of the joints between parts 10 and 13, 11 and 12, 13 and 16, and 16 and 18 can conveniently be made by spot-welding, because this gives the most satisfactory connection at an economic cost. In the case of the stiffeners 13 which are located edge-on to the mesh 10, the spot welds can be accomplished by sandwiching the stiffeners between a pair of comparatively massive bars with the stiffener edge projecting from between the bars, abutting this edge against the mesh, and locating the spot-welding electrodes against the mesh and against the co-planar edges of bars and stitfeners respectively.

The cup 18 and sleeve 20, which together constitute the pillar which suspends the anode and serves as a means for conducting the electrolysing current to it, are preferably welded together by fusion-welding so as to be liquid tight and prevent brine or other cell contents from gaining access to the bus-bar inside the pillar. The contact between the copper bus-bar and the pillar can be at any convenient point, whether at the top or base or at some intermediate point.

It will be appreciated that the pillar may be relatively massive but will not reduce the effective area of the anode because chlorine liberated at the anode in the vicinity of the pillar can pass through the mesh into the cavity 14 and exit from the cavity through openings In FIGURES 5 to 9, a sheet of titanium mesh 10 is provided with titanium stiffener strips 21 secured edge-on to the mesh on the upper face thereof. These stiffener strips have cranked ends 22 secured to a titanium block 23, which is itself separated from the mesh by a space 24 and is provided with a cavity 25 into which the supporting pillar (not shown) can be secured for example by screw threaded attachment and/or welding. In FIGURE 6, the cranked ends 22 of the stiffener strips embrace the whole of the block 23 and have their lower portions cut away below the lower surface of the block 23 to allow free communication between the space 24 and the body of the electrolyte; the extent of this cutting away may vary, and may for example correspond to two opposing sides of the block or substantially the whole circumference of the block. In FIGURES 7 and 8, the cranked ends 22 of the stiffener strips only embrace opposite sides of the block, and there is no necessity to cut away the lower portions of the cranked ends. The titanium mesh carries a layer of a platinum metal (not shown).

In operation, gas liberated at the anode surface of the mesh 10 percolates upwards through the mesh. That portion of the gas formed immediately adjacent to the block 23 first passes through the mesh 10 into the space 24, and then laterally between the lower edge of the block 23 and/or stiffener strips and the upper face of the mesh into the main body of the electrolyte, and finally into the main gas space of the cell.

The general fabrication methods which may be used are substantially the same as those applicable to the structures shown in the other drawings.

What we claim is:

1. An anode structure for the production of chlorine by electrolysis of brine, comprising an operative anode surface of a platinum metal upon mesh consisting essentially of titanium, a pillar having an imperforate lower end for suspending said mesh in the cell and conducting electrolysing current to the mesh, the end of the pillar adjacent to the mesh being spaced from the mesh so that chlorine liberated by electrolysis in the vicinity of the pillar end is not trapped but can pass through the mesh and make its way past the pillar to exit from the cell by way of the space between the mesh and the pillar end and means for supporting and spacing said pillar from said mesh and for carrying current from said pillar to said mesh, said supporting and spacing means having openings therein for the escape of said liberated chlorine gas.

2. An anode structure as claimed in claim 1 wherein the platinum metal making up the operative anode surface is selected from the group consisting of platinum, rhodium, iridium, and alloys of these metals.

3. An anode structure as claimed in claim 1, wherein the end of the pillar adjacent to the mesh is secured to end means having edges supported in spaced relationship to the mesh and secured at the edges to stifi'eners carried by the mesh.

4. An anode structure as shown in claim 3 wherein the stilfeners themselves support said end means in spaced relationship to the mesh.

5. An anode structure as claimed in claim 4 wherein the stitfeners are strips secured edge-on to the mesh.

6. An anode structure as claimed in claim 1 wherein, apart from the platinum metal surface, all parts of the structure in contact with the cell contents consist essentially of titanium.

7. An anode structure as claimed in claim 1 wherein the pillar is a tube consisting essentially of titanium.

8. An electrolytic cell for producing chlorine by the electrolysis of brine, said cell comprising a cathode and an anode structure including an operative anode surface of a platinum metal upon a mesh consisting essentially of titanium, a pillar having an imperforate lower end suspending said mesh in the cell and conducting electrolyzing current to the mesh, the end of the pillar adjacent to the mesh being spaced from the mesh so that chlorine liberated by electrolysis in the vicinity of the pillar end is not trapped but can pass through the mesh and make its way past the pillar to exit from the cell by way of the space between the mesh and the pillar end,

and means for supporting and spacing said pillar from said 5 mesh and for carrying current from said pillar to said mesh.

9. The cell of claim 8 wherein said cathode is a moving mercury cathode supported by a substantially horizontal base, said anode surface is horizontally disposed above said cathode and spaced therefrom and said pillar extends vertically upward from said mesh, said cell including means associated with said pillar for supporting said anode structure with the anode surface in operative position.

10. An electrolytic cell as claimed in claim 8 having a substantially horizontal base for supporting a moving mercury cathode.

11. The process which comprises providing brine in a cell according to claim 8 and electrolyzing the brine therein to produce chlorine.

References Cited by the Examiner UNITED STATES PATENTS 2,681,311 6/1954 DeWit 204-302 2,719,117 9/ 1955 Blue et a1. 204-270 2,974,098 3/ 1961 Oliver 204-250 FOREIGN PATENTS 616,029 3/1961 Canada.

63 1,022 11/1961 Canada. 1,217,952 12/1959 France. 1,226,153 2/1960 France.

934,044 10/ 1955 Germany.

JOHN H. MACK, Primary Examiner.

D. R. JORDAN, Assistant Examiner. 

1. AN ANODE STRUCTURE FOR THE PRODUCTION OF CHLORINE BY ELECTROLYSIS OF BRINE, COMPRISING AN OPERATIVE ANODE SURFACE OF A PLATINUM METAL UPON MESH CONSISTING ESSENTIALLY OF TITANIUM, A PILLAR HAVING AN IMPERFORATE LOWER END FOR SUSPENDING SAID MESH IN THE CELL AND CONDUCTING ELECTROLYSING CURRENT TO THE MESH, THE END OF THE PILLAR ADJACENT TO THE MESH BEING SPACED FROM THE MESH SO THAT CHLORINE LIBERATED BY ELECTROLYSIS IN THE VICINITY OF THE PILLAR END IS NOT TRAPPED BUT CAN PASS THROUGH THE MESH AND MAKE ITS WAY PAST THE PILLAR TO EXIT FROM THE CELL BY WAY OF THE SPACE BETWEEN THE MESH AND THE PILLAR END AND MEANS FOR SUPPORTING AND SPACING SAID PILLAR FROM SAID MESH AND FOR CARRYING CURRENT FROM SAID PILLAR TO SAID MESH, SAID SUPPORTING AND SPACING MEANS HAVING OPENINGS THEREIN FOR THE ESCAPE OF SAID LIBERATED CHLORING GAS. 